1. Field of the Invention
This invention relates to a wiring arrangement for printed circuit boards, and particularly to a wiring arrangement for surface mounted components utilizing twisted and non-twisted conductors.
2. Description of Background
Printed circuit boards are widely used in various electronic/electric devices such as communications equipment, control devices, household appliances, radios, televisions, washing machines, audio equipment, microwave ovens, etc. Each of these devices has enjoyed success for decades but in an ever more demanding world, requirements for their functionality continue to expand. With such expansion of capability comes the demand for higher density at the circuit board level. This can come due to size constraints or simply functional demands. As the demand for smaller, more powerful electronic systems increase, system manufacturers are tasked to find a way to increase system performance while decreasing the size of the electronic components within the electronic system.
Surface mount technology is a widely used method for constructing electronics circuits in which the components are mounted directly onto the surface of the printed circuit boards. Surface mount components are generally smaller than “through hole” mounted components and further allow for placement on both sides of the printed circuit board. Additionally, surface mounted components promote the use of automation during printed circuit board construction and therefore reduce labor costs and greatly increase production rates.
The physical dimensions of printed circuit board traces become significant relative to the wavelength of the signal at high frequencies. At these high frequencies, controlled impedance transmission lines are used to provide a path for signals from one portion of the printed circuit board to another potion of the printed circuit board. As circuit density and clock speeds increase in electronic devices, so does the need to interconnect electronic components with impedance controlled transmission lines. A current limitation in transmission lines arises when a twisted pair configuration is utilized to control the magnetic field and connect one portion of the printed circuit board to another portion of the printed circuit board. Properly forming the very precise uniform twists that make up the twisted pair is difficult to perform within the confines of printed circuit board layers having nets and vias. Additionally, many production level printed circuit boards have test ports that contain a transmission line stub connection. Stub connections are electrically undesirable as they provide a discontinuity of impedance. If the impedances are not uniform, then reflections are created that decrease signal integrity and increase electromagnetic interference (EMI). Currently, to avoid these problems, the circuit boards are either turned to remove the top side wiring or the wiring is left on the board which creates a possible reflection and radiation problem due to an antenna effect as noted above. Furthermore, removing top side wiring, or performing any rework operation on printed circuit boards, generally requires labor intensive practices that do not allow for the use of automated equipment.
Accordingly, there is a need for an improved wiring scheme that allows for ease of installation, compatibility with automated equipment, and allows for the formation of precise twisted pairs while minimizing reflections and EMI within the circuit.